Sandwich wall panels, also called integrally insulated concrete panels, are well known in the construction industry. Most sandwich panels are composed of interior and exterior concrete layers, called wythes, and one or more insulation layers between the two concrete layers. The insulation layer is generally rigid insulation, such as expanded or extruded polystyrene or polyisocyanurate. Also included in the sandwich wall panel are connectors that connect the two concrete wythes through the layer(s) of insulation. The connectors hold the components of the sandwich wall panel together and also provide a mechanism whereby loads can be transferred between the components of the wall and the structure's foundation. Common loads include tension, shear, and moments induced by wind, gravity, and seismic loads, as well as combinations thereof. In composite and partially composite sandwich wall panels, connectors must cause the two concrete wythes to function together as one structure. Depending on the application, load transfer devices may be many different shapes and composed of many different materials. One material in particular, metal, has been used in the past, but metal has undesirable thermal connectivity properties and may suffer corrosion in some situations. These problems can also be present in sandwich panels containing metal trusses or reinforcing. Accordingly, there is a need in the art for a shear connector and load transfer device that reduces the need for metal components to be used as connectors and trusses.
Alternatively, non-composite insulated concrete sandwich walls allow the components of the sandwich wall to work independently of each other. Generally, there is a structural concrete wythe, an insulation layer, and an architectural, exterior wythe. The independent behavior eliminates problems associated with large temperature differentials between interior and exterior wythes and the thermal bowing that can be present in some structural composite panels.
Sandwich wall panels can be manufactured in a variety of ways known in the art. The entire panel may be manufactured in a plant and transported to a job site, a process known as plant precast. The panel may be constructed on the ground at the job-site and then tilted up and into place, a process known as site-cast tilt-up. Sandwich walls may also be vertically cast in place at the job site, commonly known as cast-in-place construction or vertically cast in a precast factory as part of the individual rooms of a building, this method is commonly known as modular precast construction. Accordingly, the panels may be constructed in both a vertical and horizontal manner.
Also known in the industry are double wall panels, which can provide weight and structural connection improvements over traditional sandwich panels. In addition to interior and exterior concrete wythes and an insulation layer, a double wall panel also includes an air void, also called an air gap. Oftentimes, the air void is filled with concrete and/or additional insulation materials or another material upon delivery to the job site. Because double wall panels are typically lighter than sandwich panels, double wall panels may cost less to manufacture and ship. Because of these advantages, double wall panels may be manufactured to a larger size prior to shipment.
Sandwich and double wall panels may reduce the energy requirements of buildings and are becoming more popular as energy conservation is a growing concern among building owners and is increasingly present in construction codes. Integration of thicker insulation can provide even higher energy savings. Sustainable building construction is also gaining in popularity. Sandwich panels can provide means for sustainable construction by providing structural composite panels, increasing the thickness of the insulation, and reducing wythe thickness. However, sandwich panels with these features require use of either more or stronger connectors. Accordingly, there is a need in the industry for a connector to provide the strength necessary for these applications.
Green roofs are known in the industry and are growing in popularity. In this application, the roof slab should be insulated and provide a watertight surface. Oftentimes, these issues are addressed by including a layer of insulation between two concrete layers. Additionally, floor slabs present many of the same issues. The load transfer devices connecting the components of the roof and floor slabs must transfer the necessary loads and be thermally non-conductive so as to prevent condensation on the roof and floor slabs.
In addition, the double wall panels discussed above require devices such as standoff connectors to define the thickness of the double wall panel and/or support the weight of one of the concrete wythes during the manufacturing process. Accordingly, there is a need in the industry for a shear connector that can provide these functions in addition to connecting the components of the double wall panel and transferring loads between same.
As is known in the art, sandwich wall panels may be constructed either horizontally or vertically. When constructed horizontally, a first concrete layer is poured, and the insulation layer is placed on top of the wet concrete layer. The insulation layer is designed to receive the connectors or ties that will be used to interconnect the components, usually having precut or pro-machined holes. Oftentimes, these holes are much larger than the connectors themselves. This decreases the thermal efficiency of the panel and may require application of another insulation, such as foam insulation, to fill the remaining volume of the hole not taken up by the connector. Moreover, connectors of the prior art are designed to be placed between side-by-side sections of insulation, leaving behind gaps in the insulation layer that must be filled with another insulation. Accordingly, there is a need in the industry for a shear connector that will eliminate the need to fill the space remaining in the insulation after insertion of the connectors. Sandwich panels that are constructed vertically are often constructed using a method known as “cast-in-place”. In this method, the walls are created at their service location. Vertical forms are erected, and the insulation and connectors are placed into the vertical forms. The vertical forms are open at the top. Both layers of concrete are then poured simultaneously from the top of the forms. Alternatively, the concrete may be pumped into the form from one or more openings near the bottom. Accordingly, the concrete surrounds the insulation as in the horizontal methods of manufacture.
Connectors of the prior art are connected to internal reinforcing, which makes installation difficult. Accordingly, there is a need in the art for a connector that is a load transfer device that does not require connection to reinforcing or use of trusses in the wall panel and, therefore, provides ease of assembly and installation. In addition, there is a need in the art for a load transfer device that is composed of discrete load transfer members that can be selectively positioned as the application requires. Moreover, there is a need in the art for a load transfer device which provides for simple and cost-effective handling and transport.
Accordingly, a load transfer device is provided that is also a shear connector which can be used in all methods of manufacturing concrete sandwich and double wall panels, including vertical, horizontal, and modular methods. The shear connector of the present invention provides increased strength and load transfer properties over the prior art. Additionally, the present connector eliminates the need to provide foam or other insulation to fill voids left in the insulation layer after insertion of the connector. The connector is thermally nonconductive. Further, the connector can reduce or eliminate the need to include trusses that span the insulation layer. The connector can provide a standoff or spacing function during the manufacture of double wall panels. Further, the connector holds the concrete wythes of the panel from shifting during handling and transport. The connector provides for simple and cost-effective handling and transport. The load transfer device of the present application provides superior shear transfer capacity and can be placed easily in rigid insulation material.